Process for the production of malononitrile

ABSTRACT

MALONONITRILE IS PREPARED BY THE SHORT TIME HIGH TEMPERATURE REACTION OF GASEOUS ACETONITRILE AND CYANOGEN CHLORIDE IN THE MOLAR RATIO OF ACETONITRILE TO CYANOGEN HALIDE OF ABOVE 1 CHARACTERIZED IN THAT THE WELL MIXED REACTION COMPONENTS ARE REACTED AT AN AVERAGE TEMPERATURE BELOW 800*C. AND THE REACTION IS QUENCHED TO CONDENSE ACETONITRILE AND MALONONITRILE BY INTRODUCING A COOLING MEDIUM INTO THE REACTION SYSTEM.

United States Patent 3,729,499 PROCESS FOR THE PRODUCTION OF MALONONITRILE Theodor Lussling and Ferdinand Theissen, Gross-Auheim, and Wolfgang Weigert, Oifenbach, Germany, assignors to Deutsche Goldund Silber-Scheideanstalt vorrnals Roessler, Frankfurt am Main, Germany No Drawing. Filed Apr. 1, 1969, Ser. No. 812,308 Claims priority, application Germany, Apr. 5, 1968, P 17 68 154.8; Mar. 5, 1969, P 19 11 174.1 Int. Cl. C07c 121/22 US. Cl. 260-465.8 R 17 Claims ABSTRACT OF THE DISCLOSURE Malononitrile .is prepared by the short time high temperature reaction of gaseous acetonitrile and cyanogen chloride in the molar ratio of acetonitrile to cyanogen halide of above 1 characterized in that the well mixed reaction components are reacted at an average tempera ture below 800 C. and the reaction is quenched to condense acetonitrile and malononitrile by introducing a cooling medium into the reaction system.

Dixon US. Pat. 2,553,406 discloses the production of a malonitrile by the reaction of a cyanogen halide with an aliphatic mononitrile at 600700 C. for 0.5 second or more preferably for to 15 seconds. To make malononitrile itself acetonitrile is employed as the aliphatic mononitrile. In the Dixon procedure a molecular proportion of mononitrile to cyanogen halide of greater than 1 is used but the yield amounts to only about 18% Dixon US. Pat. 2,606,917 shows that introduction of inert gases such as nitrogen, carbon dioxide or steam during the reaction does not improve the yield, since a yield of only 16.5% malononitrile is obtained in experiment 7.

Further it has been disclosed in published Japanese patent application 41 16/506 (1966) that malononitrile can be produced from acetonitrile and cyanogen chloride with catalytic amounts of chlorine at 700-900 C. in the presence of inert gases. The addition of the chlorine to the cyanogen chloride should amount to 50% chlorine by weight. The yield determined only by gas chromotography amounted to about 70% based on the added cyanogen chloride.

By maintenance of the Japanese process it has been proven, however, that the yield of the isolated substance was essentially less than the yields given by gas chromatography and is 30 to 60%. Through the presence of the chlorine at the high temperature the aliphatic mononitrile becomes intermediately chlorinated and decomposes into hydrogen chloride and unknown decomposition products. These nitrile losses can amount to up to 70% of the added mononitrile. Additionally chlorine has a known corrosive effect on the apparatus so that only special materials can be used for the apparatus.

It is the object of the present invention to obtain malononitrile through the.reaction of cyanogen halide with acetonitrile with essentially higher yields of the malononitrile and almost quantitative recovery of the unreacted mononitrile.

It has now been found that malononitrile can be produced in increased yields without use of a catalyst if gaseous anhydrous or aqueous acetonitrile and gaseous cyanogen halide in the proportion of over 1 mole of acetonitrile per mole of cyanogen halide are brought into contact with each other for a short period of time at an average reaction temperature below 800 C., if necessary in the presence of inert gases, and the reaction mixture is chilled by introduction of a cooling medium whereby in the presence of water in the reaction system the reaction 3,729,499 Patented Apr. 24, 1973 mixture is neutralized during the condensation by the addition of acid binding materials.

Acetonitrile is added either in anhydrous form or containing water. Thus is can contain up to 50% by weight of water. As cyanogen halides there can be employed cyanogen halides there can be employed cyanogen chloride and cyanogen bromide. Cyanogen chloride is preferred.

The gaseous reaction partners are added in well mixed condition, e.g. through the use of known turbulent mixing processes.

The most favorable residence time is between 1 to 15 seconds, preferably 5 to 8 seconds, the most favorable average temperature is between 700 and 780 C. and the most favorable molar proportions of acetonitrile to cyanogen chloride are from 2:1 to 10:1. The reaction is generally carried out at atmospheric pressure. The lowest average temperature is 550 C.

As inert gases there can be added nitrogen, carbon dioxide or steam. The inert gas, when employed, is added in an amount of 0.2% to 70% of the total volume of gases. Steam is especially important since in this case the inert gases are condensible and the losses of unchanged addition products and the arising final product are essentially reduced. Further in the presence of steam a definite increase in yield is noted, based on the reacted cyanogen chloride and based on the reacted acetonitrile.

The gases leaving the reaction can be chilled by any cooling means which either does not introduce impurities into the end product or which can be easily removed from it. Thus there can be used the condensing malononitrile itself, or also water or acetonitrile. Also there can be used as the cooling means acetonitrile containing up to 50% water by weight. The cooling means can be introduced into the reaction mixture is known manner, advantage ously by injection. The cooling medium quenches the product quickly to below C.

The water introduced as addition product inert gas or cooling means during the course of the reaction forms aqueous hydrochloric acid from the hydrogen chloride arising from the reaction. This can saponify the malononitrile produced. For this reason the reaction mixture dur ing the cooling is simultaneously neutralized. As the neutralization means there are preferably used substances which in the reaction with hydrochloric acid, form chlorides having drying properties. Especially suitable are alkali or alkali earth metal carbonates or bicarbonates, most preferably lithium, magnesium and calcium. These can be added alone or in admixture. If the chlorides formed which act as driers there is obtained a practically water free reaction product. Specific examples of suitable additives include lithium carbonate, lithium bicarbonate, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, magnesium carbonate, calcium carbonate, strontium carbonate and barium carbonate. Less preferably there can be used alkali metal and alkaline earth metal hydroxide and oxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, barium hydroxide, lithium oxide, sodium oxide, potassium oxide, magnesium oxide, calcium oxide and barium oxide. Neutralization need only be to a pH of 0 to about 2. Mixtures of neutralizing agents can be employed.

The formation of such chloride is always very suitable if the content of yvater or steam amounts to 10 to 30% by weight of the acetonitrile at a molar ratio of acetonitrile to cyanogen chloride of from 8:1 to 2:1. The cooled and with the use of water neutralized mixture is distilled in the customary way. The yields of product amount to 67.0 to 82.5% based on the reacted cyanogen chloride and up to 83% based on the reacted acetonitriles.

The technical improvement of the process of the invention primarly lies in a substantial increase in the yield of material without additional technically employed precautions.

It has further been found that an increase in yield occurs in reference to the added acetonitile if the condensation of the reaction mixture takes place immediately inside the reactor outlet that is if the cooling means for the quenching also is introduced immediately into the reactor outlet. If aqueous solutions are added as quenching means or if steam is in the system, eg by addition of water containing acetonitrile then the formed hydrogen chloride must be neutralized immediately after the introduction of the condensation means. In this regard by neutralization a pH of to about 2 is meant. Higher pH values are not necessary if the layers built by the condensation and neutralization are immediately separated.

A phase separation is always possible if a salt solution concentrated as high as feasible is present after the neutralization as a result of reaction of the neutralization agent and the hydrogen chloride.

The neutralization agent is preferably added as a solid. The amount of water in the system should therefore preferably be so added that after the neutralization concentrated salt solutions result, in order that the separation is made easier. By the continuous carrying out of the process, if necessary, fresh water is added corresponding to the amount of salt formed and a corresponding amount of aqueous salt solution is removed. This salt solution is distilled to recover the acetonitrile dissolved therein. In place of fresh water partially aqueous crude acetonitrile can be added as it is produced in other chemical processes. The acetonitrile then resulting from the working up of the reaction product serves without further purification as the starting material for the malononitrile synthesis. The impurities introduced into the crude malononitrile through the crude acetonitrile anyhow are separated by the necessary purification of the nitrile without additional difficulty. It further appears that a very thorough mixing of the starting products is essential as well as a removal of the coating arising through cracking on the reactor outlet.

Unless otherwise indicated all parts and percentages are by weight.

EXAMPLE 1 Gaseous acetonitrile and cyanogen chloride were brought to reaction in the presence of nitrogen in a ceramic reactor at an average temperature of about 750 C. and a maximum temperature of 820 C. in the reaction mixture, after the gases had previously been intimately mixed. The gases were added in the molar proportions of acetonitrile to cyanogen chloride to nitrogen of 5.1:l:2.1. The gaseous mixture was in the reaction zone for 6.9 seconds. The reaction product was then introduced into ice water cooled acetonitrile and finally fractionally distilled in a vacuum. There were employed 0.1 part of the ice water cooled acetonitrile for each part of cyanogen chloride in the initial mixture. Through the distillation malononitrile was isolated as a water white product in a 66.6% yield based on the reacted cyanogen chloride and a 30% yield based on the reacted acetonitrile.

EXAMPLE 2 In the same reactor as in Example 41 a well homogenized mixture of acetonitrile, cyanogen chloride and steam were reacted at an average temperature of 773 C. and a maximum temperature of 825 C. The amount of water was 15% based on the weight of the acetonitrile. The acetonitrile and cyanogen chloride were in the molar proportions of 5.54:1. The residence time of the gaseous mixture in the reaction zone was 6.9 seconds. The product gases leaving the reactor were neutralized during the condensation with pieces of marble. There were used 2.35 parts of marble per part of cyanogen 4 chloride. The reaction mixture was worked in the manner described in Example 1. The yield of water white malononitrile amounted to 71.6% based on the cyanogen chloride reacted and 60.1% based on the acetonitrile reacted.

EXAMPLE 3 The process of Example 2 was employed using acetonitrile and cyanogen chloride in the molar proportions of 5.75:1. The actonitn'le contained 27.2% water. The residence time was 6.8 seconds. The yield of malonitrile was 67.0% based on the cyanogen chloride reacted and 63% based on the acetonitrile reacted.

EXAMPLE 4 In the same reactor as in Example 1 acetonitrile containing 15% water was reacted with cyanogen chloride at an average temperature of 770 C. and a maximum temperature of 820 C. and a residence time of the gas mixture in the reaction zone of 6.54 seconds. The molar proportions of acetonitrile to cyanogen chloride were 3.92:1. The gases leaving the reactor were condensed by injecting aqueous acetonitrile having a temperature of 20 C. and simultaneously neutralized with calcium carbonate. There were employed 152 parts of water and 2399 parts of acetonitrile in the cooling mixture and 235 parts of calcium carbonate as the neutralizing agent. The yield of water white malononitrile amounted to 74.5% based on the cyanogen chloride reacted and 57.2% based on the acetonitrile reacted.

EXAMPLE 5 In the same reactor as Example 1 anhydrous acetonitrile was reacted with cyanogen chloride in the molar proportions of 4.211 at an average temperature of 780 C. and a maximum temperature of 820 C. and a residence time of the gases in the reaction zone of 7.8 seconds. The gases leaving the reactor were simultaneously neutralized with 2.59 parts of calcium carbonate per part of cyanogen chloride employed and condensed through injection of aqueous acetonitrile having a temperature of 20 C. and containing 0.94 part of water and 13.3 parts of acetonitrile per part of cyanogen chloride employed. The yield of water white malonitrile amounted to 80.1%, based on the cyanogen chloride reacted and 65% based on the acetonitrile reacted.

EXAMPLE 6 In the same reactor as Example 1 anhydrous acetonitrile was reacted with cyanogen chloride in the molar proportions of 4.45:1 at an average temperature of 776 C. and a maximum temperature of 820 C. and a residence time of the gases in the reaction zone of 7.7 seconds. The gas leaving the reactor was condensed by injecting 16.5 parts of acetonitrile based on the starting cyanogen chloride. The following fractional distillation resulted in a malononitrile yield of 77% based on the cyanogen chloride reacted.

EXAMPLE 7 In the same reactor as Example 1 anhydrous acetonitrile was reacted with cyanogen chloride in the molar proportions of 6.78:1 at an average temperature of 780 C. and a maximum temperature of 820 C. and a residence time of 8.04 seconds. The gases leaving the reactor were condensed through 1000-1400 parts of circulating water based on the cyanogen chloride employed at a temperature of 2030 C. and simultaneously neutralized with 2.8 parts of calcium carbonate based on the starting cyanogen chloride. The water contained acetonitrile and the reaction product corresponding to their solubility. After working up in the manner of Example 1 malononitrile was isolated as a water white product in a yield of 80.5% based on the cyanogen chloride reacted and a yield of 64.2 based on the acetonitrile reacted.

EXAMPLE 8 In the same reactor as Example 1 acetonitrile containing 15% water was reacted With cyanogen chloride in the molar proportions of 2.12:1 at an average temperature of 780 C. and a maximum temperature of 820 C. and a residence time of 6.25 seconds. The gases leaving the reactor were quenched by injection of aqueous acetonitrile containing 0.87 part water and parts acetonitrile based on the cyanogen chloride employed and were simultaneously neutralized with 2.1 parts of calcium carbonate based on the cyanogen chloride employed. The customary working up gave a yield of 66.2% water white malononitrile based on the cyanogen chloride reacted and 65.0% based on the acetonitrile reacted.

EXAMPLE 9 In the same reactor as Example 1 acetonitrile and cyanogen chloride were reacted in the molar proportions of 3.9:1 at an average reaction temperature of 775 C. and a residence time of 7.3 seconds. The acetonitrile, containing as primary impurities 3.91% hydrogen cyanide and 3.43% water consisted of recycled acetonitrile which was obtained as low boiling fraction (B.P. lower than 40 C.) during the work up of the reaction products and which had been dried partially with calcium chloride. For reacted acetonitrile aqueous crude acetonitrile was supplied by introducing it into the quenching system. The reaction gases leaving the reactor were quenched in the reactor outlet through the injection of the circulating aqueous phase at a temperature of 20-30 C. and in an amount of 1000-1400 parts per part of cyanogen chloride employed, and at the same time neutralized with calcium carbonate to a pH of 0.5. The aqueous phase formed on account of the salting out elfect of the calcium chloride which arose from the neutralization of hydrochloric acid with calcium carbonate. After working up the organic phase in a vacuum and recovery of the ace tonitrile dissolved in the salt containing water malononitrile was recovered in a yield of 82.5% based on the cyanogen chloride reacted and in a yield of 83% based on the acetonitrile reacted.

In the process of the present invention the unreacted acetonitrile after separation from malononitrile is recycled for reaction with cyanogen chloride.

What is claimed is:

1. In a process for the catalyst free production of malononitrile in a reactor by the short time reaction of reactants consisting essentially of gaseous acetonitrile and gaseous cyanogen halide selected from the group consisting of cyanogen chloride and cyanogen bromide in the molar ratio of the above one mole of acetonitrile to one mole of cyanogen halide the improvement comprising intimately mixing the reaction components, reacting said intimate mixture of reaction components at an average temperature below 800 C. but not lower than an average temperature of 550 C. and quenching the reaction to below 75 C. to condense acetonitrile and malononitrile by introducing a cooling medium by chemical contact into the reaction mixture.

2. A process according to claim 1 wherein the maximum temperature is 825 C., the cooling medium is a member of the group consisting of malononitrile, water, anhydrous acetonitrile and aqueous acetonitrile, the molar proportions of acetonitrile to cyanogen halide are between 2:1 and 10:1 and the residence time in the reactor is 1 to 15 seconds.

3. A process according to claim 2 wherein the reaction mixture is neutralized with an alkali metal or alkaline earth metal carbonate, bicarbonate, oxide or hydroxide.

4. A process according to claim 1 wherein the cooling medium is one which does not introduce impurities into the end product.

5. A process according to claim 1 wherein the time in the reactor is 1 to 15 seconds.

6. A process according to claim 5 wherein the average temperature is 700" to 780 C.

7. A process according to claim 1 wherein water is present in the reaction system and the reaction mixture is neutralized during the condensation by the addition of acid binding material.

8. A process according to claim 1 in which the cyanogen halide is cyanogen chloride.

9. A process according to claim 8 wherein the ace tonitrile reactant contains water in an amount up to 50%.

10. A process according to claim 8 wherein as the cooling medium there is employed a member of the group consisting of malononitrile, water, anhydrous acetonitrile and aqueous acetonitrile.

11. A process according to claim 10 wherein Water is present in the reaction system after introduction of the cooling medium and the neutralization of the reaction mixture is accomplished by introducing a carbonate of the group consisting of lithium, magnesium and calcium carbonate.

12. A process according to claim 8 wherein the molar proportions of acetonitrile to cyanogen chloride are between 2:1 and 10:1.

13. A process according to claim 12 wherein the residence time in the reactor is 1 to 15 seconds.

14. A process according to claim 8 wherein the quenching of the reaction mixture with the cooling medium occurs immediately at the outlet of the reactor.

15. A process according to claim 14 wherein as the cooling medium there is employed a member of the group consisting of malononitrile, water, anhydrous acetonitrile and aqueous acetonitrile.

16. A process according to claim 8 wherein water is present in the reaction system after introduction of the cooling medium and neutralization of the reaction mixture is accomplished by introducing an acid binding alkali metal or alkaline earth metal compound.

17. A process according to claim 16 wherein unpurified acetonitrile is introduced as the cooling medium.

References Cited UNITED STATES PATENTS 2,553,406 5/1951 Dixon 260465.8 3,417,126 12/1968 Taguchi et al. 260465.8 3,541,133 11/1970 Johnson et a1. 260465.8 R

JOSEPH P. BRUST, Primary Examiner 

